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FreeBSD-SA-16:37.libc                                       Security Advisory
                                                          The FreeBSD Project

Topic:          link_ntoa(3) buffer overflow 

Category:       core
Module:         libc
Announced:      2016-12-06, revised on 2016-12-08
Affects:        All supported versions of FreeBSD.
Corrected:      2016-12-07 23:19:46 UTC (stable/11, 11.0-STABLE)
                2016-12-07 23:29:42 UTC (releng/11.0, 11.0-RELEASE-p5)
                2016-12-07 23:20:26 UTC (stable/10, 10.3-STABLE)
                2016-12-07 23:31:07 UTC (releng/10.3, 10.3-RELEASE-p14)
                2016-12-07 23:32:42 UTC (releng/10.2, 10.2-RELEASE-p27)
                2016-12-07 23:34:06 UTC (releng/10.1, 10.1-RELEASE-p44)
                2016-12-07 23:20:50 UTC (stable/9, 9.3-STABLE)
                2016-12-07 23:35:15 UTC (releng/9.3, 9.3-RELEASE-p52)
CVE Name:       CVE-2016-6559

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

0.   Revision history.

v1.0  2016-12-06 Initial release.
v1.1  2016-12-08 Revised patches to address regressions.

I.   Background

The link_ntoa(3) function generates ASCII representation of a link-level
address and is avaliable as part of standard C library (libc).

II.  Problem Description

A specially crafted argument can trigger a static buffer overflow in the
library, with possibility to rewrite following static buffers that belong to
other library functions.

III. Impact

Due to very limited use of the function in the existing applications,
and limited length of the overflow, exploitation of the vulnerability
does not seem feasible.  None of the utilities and daemons in the base
system are known to be vulnerable.  However, careful review of third
party software that may use the function was not performed.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Restart all daemons that use the library, or reboot the system.

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[*** v1.1 NOTE ***] If your sources are not yet patched using the initially
published patch, then you need to apply libc.patch.  If your sources are
already updated, or patched with patch from the initial advisory, then you
need to apply the incremental patch, named libc-inc.patch.

[FreeBSD system, not patched with initial SA-16:37 patch]
# fetch https://security.FreeBSD.org/patches/SA-16:37/libc.patch
# fetch https://security.FreeBSD.org/patches/SA-16:37/libc.patch.asc
# gpg --verify libc.patch.asc

[FreeBSD system, initial SA-16:37 patch already applied]
# fetch https://security.FreeBSD.org/patches/SA-16:37/libc-inc.patch
# fetch https://security.FreeBSD.org/patches/SA-16:37/libc-inc.patch.asc
# gpg --verify libc-inc.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

Restart all daemons that use the library, or reboot the system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r309691
releng/9.3/                                                       r309697
stable/10/                                                        r309690
releng/10.1/                                                      r309696
releng/10.2/                                                      r309694
releng/10.3/                                                      r309693
stable/11/                                                        r309689
releng/11.0/                                                      r309692
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:http://www.kb.cert.org/vuls/id/548487>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6559>
<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=215105>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:37.libc.asc>
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